1. Field of the Invention
The present invention relates to an antiglare film provided on the display surface side of a high-resolution image display device such as a CRT or LCD used for image display in a computer, word processor, television monitor, or the like. The present invention relates also to a method for fabricating an antiglare film, and to a polarizer element and a display device employing an antiglare film. The present invention relates, in addition, to an internal diffusion film.
2. Description of the Prior Art
Conventionally, display devices as mentioned above are used for image display in computers, word processors, television monitors, and the like. In recent years, as higher and higher resolutions are sought in applications such as in monitors for computers, display devices have come to be given higher and higher resolutions. The pace of this trend is especially fast in LCDs, where remarkable technical developments have been made in connection with p-Si. Such a display device is generally provided, on the display surface side thereof, with an antiglare film treated with various kinds of antiglare treatment. This helps reduce the glare resulting from reflection of external light as from a window or indoor illumination and the glare resulting from light emanating from within the display device.
Conventional examples of such antiglare films are as follows. Japanese Patent Application Laid-Open No. H6-18706 discloses an antiglare layer formed on a transparent substrate and consisting essentially of resin beads having a refractive index of 1.40 to 1.60 and an ionizing-radiation-curable resin composition. Japanese Patent Application Laid-Open No. H10-20103 discloses a multilayer film consisting of at least a base film and an antiglare layer containing 20 to 30 parts by weight of transparent particles having an average particle diameter of 0.5 to 1.5 μm in 100 parts by weight of curable resin.
These antiglare films are formed by applying a resin containing a filler such as silicon dioxide (silica) to the surface of a transparent base film. These antiglare films are grouped into those in which surface irregularities are formed on the surface of the antiglare layer by coagulation of coagulative silica or the like, those in which surface irregularities are formed on the layer surface by addition, to the resin, of an organic filler having a particle diameter greater than the thickness of the applied resin film, those in which surface irregularities are transferred by laminating the layer surface with a film having surface irregularities, and the like.
On the other hand, Japanese Patent Application Laid-Open No. 2001-91707 discloses an optical film having an antiglare layer laid on a transparent support member wherein the antiglare layer has a haze of 4.0 to 50.0%, where the haze is defined as the total of internal diffusion of 1.0% or higher and surface diffusion of 3.0% or higher. This is an antiglare film employing an internal diffusion layer, which has fine particles dispersed inside the layer to cause diffusion.
However, the structures disclosed in Japanese Patent Application Laid-Open No. H6-18706 and Japanese Patent Application Laid-Open No. H10-20103 mentioned above both depend solely on the surface irregularities on the antiglare layer to produce an antiglare effect. Thus, to enhance the antiglare effect, the surface irregularities need to be made larger. However, making the surface irregularities larger results in increasing the haze value (diffused-light transmittance divided by total transmittance) of the applied resin film. This lowers the sharpness of the transmitted image accordingly.
Moreover, when an antiglare film of a conventional type as described above is used on the display surface side of a high-resolution image display device, random shining, called scintillation, occurs. This lowers the viewability of the display surface. Scintillation occurs as a result of the curvatures of the surface irregularities serving as lenses, magnifying pixels when their positions happen to coincide with the foci of those lenses. In an antiglare film of a conventional type, the surface irregularities are formed randomly, and therefore it is impossible to control the foci of the lenses they pretend to be, making scintillation inevitable.
On the other hand, the structure disclosed in Japanese Patent Application Laid-Open No. 2001-91707 prevents light from traveling straight inside the layer, and thus suffers less from scintillation. However, the display performance obtained here is dependent on viewing angle. Specifically, when this structure is used in a display device in which light leaks obliquely during display of black, light leaking obliquely is deflected to travel straight forward. This lowers the contrast ratio as observed frontally.